The Race To Make Quantum Computers

We still don't quite have a truly-accepted working model, even from D-Wave. So it is interesting to see this latest news of both Google and IBM launching projects to produce and eventually sell these quantum computers.

The folks from Google's Quantum AI Laboratory wrote a comment in Nature, while IBM's intention is reported in the news.

With the Chinese company Alibaba collaborating with the Chinese Academy of Sciences to also go into this area, the next several years will be fascinating to watch.

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Teleportation to a Solid-State Quantum Memory

The Gisin group has done it again! This time, they have managed to teleport a quantum state via photons and into a quantum memory in a form of a doped crystal.

Today, Felix Bussières at the University of Geneva in Switzerland and a few pals say they’ve taken an important step towards this. These guys have teleported quantum information to a crystal doped with rare-earth ions—a kind of quantum memory. But crucially they’ve done it for the first time over the kind of ordinary optical fiber that telecommunications that are in use all over the world.

This work has been published in Nature Photonics.

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An Actual Test To Verify A Quantum Computer?

We may just have one, according to this Wired article.

In the April 25 issue of the journal Nature, Vazirani, together with Ben Reichardt of the University of Southern California in Los Angeles and Falk Unger of Knight Capital Group Inc. in Santa Clara, showed how to establish the precise inner state of such a computer using a favorite tactic from TV police shows: Interrogate the two components in separate rooms, so to speak, and check whether their stories are consistent. If the two halves of the computer answer a particular series of questions successfully, the interrogator can not only figure out their internal state and the measurements they are doing, but also issue instructions that will force the two halves to jointly carry out any quantum computation she wishes.

Wonder if the D-Wave people would like to subject their machines to such a test?

The article also has some coverage of quantum entanglement and the basics of quantum computation.

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Solving A Simple Simultaneous Equation Using Quantum Computer

This work appears in this week's PRL. A group of scientists have managed to solve a rather simple simultaneous equation with two variables using a quantum computation scheme proposed back in 2009.

The computational feat has been carried out by Jian-Wei Pan and colleagues at the University of Science and Technology of China, the University of Toronto and the National University of Singapore, who used a quantum algorithm created in 2009 by Aram Harrow, Avinatan Hassidim and Seth Lloyd. For simple systems of linear equations, Harrow and colleagues showed that their algorithm can be exponentially faster than the best solving methods that use a classical computer. One important caveat, however, is that the algorithm does not find an exact solution, but only the most likely answer.

Most likely answer, eh? Not sure how good that will be especially when we use computers to solve already-uncertain situations such as weather forecasting and other phenomena.

Still, this is merely a baby step in the evolution of quantum computers.

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Ions Entangled Using Microwaves

In what is claimed to be a major breakthrough, ions have been trapped and entangled using microwaves for the first time. Supposedly, this is significant because one can deal with microwaves in electrical circuits, and certainly easier than using optical frequency lasers.

Two independent groups of physicists have made important breakthroughs in the control of quantum computers based on trapped ions. Instead of controlling quantum bits (qubits) using multiple laser beams, the teams have used microwave sources, which are much easier to control and integrate within quantum circuits. The work could lead to practical quantum computers that incorporate large numbers of qubits on a single chip.

Progress is often made in small steps. This is another example of it.

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Random Numbers Certified by Bell’s Theorem

Haven't had time to closely read this yet, but it is a good one.

Abstract: Randomness is a fundamental feature of nature and a valuable resource for applications ranging from cryptography and gambling to numerical simulation of physical and biological systems. Random numbers, however, are difficult to characterize mathematically, and their generation must rely on an unpredictable physical process. Inaccuracies in the theoretical modelling of such processes or failures of the devices, possibly due to adversarial attacks, limit the reliability of random number generators in ways that are difficult to control and detect. Here, inspired by earlier work on non-locality-based and device-independent quantum information processing, we show that the non-local correlations of entangled quantum particles can be used to certify the presence of genuine randomness. It is thereby possible to design a cryptographically secure random number generator that does not require any assumption about the internal working of the device. Such a strong form of randomness generation is impossible classically and possible in quantum systems only if certified by a Bell inequality violation15. We carry out a proof-of-concept demonstration of this proposal in a system of two entangled atoms separated by approximately one metre. The observed Bell inequality violation, featuring near perfect detection efficiency, guarantees that 42 new random numbers are generated with 99 per cent confidence. Our results lay the groundwork for future device-independent quantum information experiments and for addressing fundamental issues raised by the intrinsic randomness of quantum theory.

S. Pironio et al., Nature v.464, p.1021 (2010).

A news report on this paper can be found here.

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Quantum Computer Gets Hydrogen Molecule Right

This is rather amazing, at least, it is to me.

A new report has shown proof-of-principle of using a quantum computer algorithm and applying it to photons to calculate and simulate the hydrogen molecule.

Reporting online January 10 in Nature Chemistry, the Harvard group, led by chemist Alán Aspuru-Guzik, developed the conceptual algorithm and schematic that defined the computer’s architecture. Aspuru-Guzik has been working on such things for years but didn’t have the hardware to test his ideas. At the University of Queensland, physicist Andrew G. White and his team, who have been working on such sophisticated gadgets, said they thought they could make one to the Harvard specs and, after some collaboration, did so. In principle the computer could have been rather small, “about the size of a fingernail,” White says. But his group spread its components across a square meter of lab space to make it easier to adjust and program.

The reference to the actual Nature Chemistry paper is as follows:

B.P. Lanyon et al, Nature Chemistry v.2, p.106 (2009).

This is outstanding work! I'd love to see the setup and even better if I get to see it running.

Sidenote: why is this published online in 2010, but it has a reference dated 2009? Usually, the online publication is well ahead of the actual publication.

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Quantum Algorithms for Algebraic Problems

A very extensive review of quantum algorithms, and more importantly, an exploration on what type of mathematical problems that can be more efficiently solved using computer computers versus classical computers[1].

Abstract: Quantum computers can execute algorithms that dramatically outperform classical computation. As the best-known example, Shor discovered an efficient quantum algorithm for factoring integers, whereas factoring appears to be difficult for classical computers. Understanding what other computational problems can be solved significantly faster using quantum algorithms is one of the major challenges in the theory of quantum computation, and such algorithms motivate the formidable task of building a large-scale quantum computer. This article reviews the current state of quantum algorithms, focusing on algorithms with superpolynomial speedup over classical computation and, in particular, on problems with an algebraic flavor.

The arXiv version can be found here.

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[1] A.M. Childs and W. van Dam, Rev. Mod. Phys. v.82, p.1 (2010).

Google Exploring Quantum Computing Algorithms

Google is probably the first major internet company to explore quantum computing algorithms, based on this report.

Google is working on developing a quantum computer, announced Google's Hartmut Neven at the Neural Information Processing Systems conference (NIPS 2009) in Vancouver, Canada last week.

Nevan, who is the comapny's technical lead manager for image recognition gave details of the presentation on the google research blog.

The reason for google's interest in quantum computing is speed. At the size of the internet increases exponentially it is becoming harder and harder for google to maintain the fast speed of the service without having to resort to building massive server farms.

They certainly have the financial resources to explore such research-front area. Companies with money can do that, as we have seen with Bell Labs during the golden days when it has the money and the monopoly.

But hold on. After reading some more of the article, my eyes widened when I read something a bit unsettling.

The company has spent three years working on quantum adiabatic algorithms with a Canadian company D-Wave providing the hardware.

D-Wave's processors work by magnetically coupling superconducting loops called rf-squid flux qubits. "It is not easy to demonstrate that a multi-qubit system such as the D-Wave chip indeed exhibits the desired quantum behavior," says Nevan.

D-Wave, D-Wave, D-Wave... I know that company. They claimed to have made the first "quantum computer", a claim that has yet to be verified (read here, here, and here. Anyone has any new update on them?).

Interesting!

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How Fundamental Particles Lose Track Of Quantum Mechanical Properties

We have another report on the study on the mechanism of the differences between the quantum world and our classical world. This is another study on the effect of decoherence on a quantum system that couples to an external "bath".

It would be interesting to compare this to an earlier report on the emergence of a classical system from a single-particle state after just one interaction. It is also interesting to see how Roger Penrose would handle this. He seems to think that our classical world emerges due to some coupling or interaction between the quantum systems and gravity, and that eventually destroys the quantum system and out comes the classical system. These two papers above seems to indicate that the mere act of decoherence might be sufficient to produce the classical world.

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Physicists Successfully Store and Retrieve Nothing

This could easily fit in as an episode of the Jerry Seinfeld series.

It appears that there is such a thing as a "squeezed vacuum", and it takes some effort to store and retrieve this "nothingness".

To see what this is, begin with a normal light wave. Classically, this is a smooth wave of electromagnetic fields with equally spaced peaks and dips. But throw in quantum mechanics and things get more complicated. The precise height of the wave becomes uncertain, so the wave gets fuzzy (see figure). Physicists have learned how to manipulate that inevitable uncertainty--for example, making it smaller at the peaks and larger in between. That makes "phase-squeezed light." Now imagine turning down the intensity of the phase-squeezed light to zero. The wave itself goes away, but the waxing and waning uncertainty remains, creating a squeezed vacuum.

It's interesting that two separate groups produced work on this at almost the same time. This, of course, is not unusual, and PRL, Nature, and Science have been known to put such things in the same issue. It serves to reinforce the discovery.

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Scientists Make Key Steps Towards Quantum Computer

NEC scientists in Japan made key steps towards the realization of quantum computers.

In what they claimed was a world first, researchers at NEC and the state-funded Institute of Physical and Chemical Research successfully demonstrated a circuit that can control the state of a pair of elemental particles and how strongly they interact with one another.

And unlike the recent unverified claims by D-Wave systems, they are actually publishing this like any scientific work, and in Science no less.

Quantum Coherent Tunable Coupling of Superconducting Qubits
A.O. Niskanen, et al., Science v.316, p.723 (2007)

Abstract: To do large-scale quantum information processing, it is necessary to control the interactions between individual qubits while retaining quantum coherence. To this end, superconducting circuits allow for a high degree of flexibility. We report on the time-domain tunable coupling of optimally biased superconducting flux qubits. By modulating the nonlinear inductance of an additional coupling element, we parametrically induced a two-qubit transition that was otherwise forbidden. We observed an on/off coupling ratio of 19 and were able to demonstrate a simple quantum protocol.

Maybe D-Wave Systems could learn from these people.

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More Brian Greene Interview

This guy is in the news almost as much as Stephen Hawking! :)

This time, Greene is being interviewed because he was brought in as a "consultant" for the upcoming movie Deja Vu, one of the upcoming Jerry Bruckheimer movie. So read it and weep. You probably won't see physics being discussed on a movie website anytime soon!

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Even More Review of That "Quantum Computer"

We have had many news media reporting on this already. So here's one more. The New York Times has a lengthy report on what has transpired, and the perception within the relevant scientific community about D-wave claims. There is really nothing new here, with D-wave systems still showing utter disregard to supporting its claim on physical grounds.

I find the picture in the article rather funny and "generic". Why do they always want to take pictures of the crygenic tanks? :)

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More Update on That "Quantum Computer"

After the dust has settled a little bit, we are starting to find out a bit more about D-Wave's "quantum computer". A new report on PhysicsWeb has delved into the matter even more closely, and presented a better picture of what could possibly be the mechanism involved in this so-called quantum computer. It certainly is a step in the right direction. However, I don't think this is that big of a step because there appears to be a fundamental scaling issue that has yet to be solved. This, and the need to maintain coherence of the system, are the two of the major issues in quantum computing. I don't see that they have yet solved this.

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Update on That "Quantum Computer"

This week's issue of Nature [Nature 446, 245 (15 March 2007)] has a follow up on the recent claim by D-Wave systems of building the first working quantum computer.

D-Wave's approach is known as adiabatic quantum computing. It uses a superconducting microchip to create spinning loops of current, which it says act as qubits, spinning in both directions at once. The qubits then entangle together, putting the entire machine in a 'quantum ground state'. By slowly changing the magnetic fields around the qubits, the computer's operator can then change the computer's entanglement, moving it into a new ground state. Reading this state can, according to the designers, reveal a solution to a complex problem without the need to directly read the state of individual qubits.

My initial reaction to this was how they were hoping to isolate the system and preserves the entanglement. It seems that I'm not the only one who is skeptical on this particular issue.

Aaronson says, however, that external noise could still be a problem for the machine. He also notes that the company has provided no public evidence that it has its system under control — or that its qubits are entangled correctly. According to Lloyd, researchers are still debating whether the entire approach is of any use: "Nobody knows exactly whether adiabatic quantum computing will work or not.

The most amusing part of this article was the response by Geordie Rose, D-Wave's founder and chief technology officer.

But Rose says that the company's scientists are satisfied that the system is indeed operating properly — and that the objective is to try something out and see whether it works, rather than to pin down exactly how it does so. "I understand the scientific community would like to see publications coming from us," he says. "But this project has never been about science, it's about building a machine."

Now, to be fair, he is right at some level. If he can show to some extent that it "works", then he could have said that he created a "computer". However, if he claims that this is a "quantum computer", then this is a different matter. This requires the demonstration that you ARE using the prescribed quantum effects as the mechanism to to produce the result. Considering that this is still a new and unexplored area, making such a claim DOES require scientific verification. Simply saying something like "I have a box, and it spits out results, and so it works" will not cut it, and certainly not if you want to convince that you not only have a box that works, but a box that works using a particular methodology! That is now a different animal than just engineering.

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Was It Really A Quantum Computer?

I reported earlier in the week about the brouhaha surrounding D-Wave System's impending announcement of a "quantum computer". As expected, it isn't a done deal, and many experts not only argue that it isn't really a quantum computer, but also that what was revealed is slower than conventional computers.

Why am I not surprised?

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Quantum Computer To Be Unveiled Tomorrow?

That soon?

A Canadian company, D-Wave Systems, has announced the unveiling of what it has called its "quantum computer" tomorrow (Tuesday). Of course, there's a chorus of "yeah, right!" coming from many corners.

So far, the details are sketchy (and we all know that the devil (god?) is in the details). Just because someone calls it something doesn't make it what it is supposed to be (i.e. quantum "teleportation"). Still, how many want to bet that this is really the "quantum computer" that we all had in mind?

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Quantum Criticality

Quantum critically is one of the most important principle in condensed matter physics (high-Tc superconductors, for example, exhibits properties that indicate that its phase is close to such criticality). To mark last year's World Year of Physics 2005, Piers Coleman and Andrew Schofield wrote a summary of Einstein's contribution to the physics of solids, from the point of view of his contribution to quantum criticality. The article was published in Nature, but you can get a copy of it here.

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